It will be very helpful yes! But, I think, It will be better re-engine Post (and customs), Page, Tax (tags and categs), Users and Comments to become a same kind of object with a special attribute to define their type and another attribute for link objects between them and, of course, able to include any kind of custom meta data for each one. Imagine, you will be able to declare any meta data to any kind of object and use the same WP_Query to work with these objects and able to link any kind of object to other. For example, you will be able to link a comment with a user or a tax; or a user with a Page or category. This last, like Post 2 Post plug-in does, but, till today, for post and users only.